The Role of Ethylene Glycol in HVAC Systems

Ethylene glycol is the standard heat transfer fluid for industrial and commercial glycol in HVAC systems. By lowering the freezing point of water, glycol prevents catastrophic pipe bursts during winter shutdowns or low-ambient operations. Beyond freeze protection, a properly maintained ethylene glycol solution stabilizes system pressure and ensures consistent heat exchange across chiller coils.

Inhibited vs Uninhibited Glycol: Why It Matters

Plant operators frequently ask about inhibited vs uninhibited glycol. Uninhibited ethylene glycol degrades over time into highly acidic byproducts, specifically glycolic and formic acids. This drops the system pH and rapidly corrodes copper, steel, and brass components.

Inhibited glycol contains specialized buffering agents (such as dipotassium phosphate) that neutralize these acids and passivate metal surfaces. Always use 100% Ethylene Glycol Inhibited for closed-loop HVAC chillers. Using uninhibited technical-grade glycol will destroy a chiller's heat exchanger within months.

Ethylene Cooling: Heat Transfer Efficiency

For ethylene cooling applications, thermal conductivity and viscosity dictate pump sizing and flow rates. Ethylene glycol has a lower viscosity than propylene glycol at low temperatures, requiring less pumping energy to circulate through the system.

However, adding any glycol to water reduces its specific heat capacity. A 30% ethylene glycol solution transfers heat about 10% less efficiently than pure water. Operators must compensate by increasing flow rates or accepting a slight derating of the chiller's total cooling capacity.

Propylene vs. Ethylene Glycol in Chillers

When selecting a heat transfer fluid, operators must compare the physical properties of ethylene and propylene glycol. Ethylene glycol offers superior heat transfer and lower viscosity, making it the standard for industrial chillers. Propylene glycol is less toxic, making it mandatory for food processing facilities or areas where incidental environmental contact is a risk.

Proper Dilution with Deionized Water

Never dilute glycol with tap water. The calcium, magnesium, and chlorides in municipal water react with the inhibitor package, causing it to drop out of solution as abrasive sludge.

Always mix glycol with Deionized Water. With a boiling point of 100°C and zero dissolved solids, DI water preserves the chemical integrity of the corrosion inhibitors and prevents scale buildup inside the chiller tubes.

Maintenance and Testing Protocols

Routine testing prevents unexpected downtime and extends the life of the chiller system. Follow these three core testing protocols:

• Concentration: Measure using a glycol refractometer. Hydrometers are inaccurate and should not be used for industrial systems.
• pH Levels: Maintain a pH between 8.0 and 9.5. A drop below 8.0 indicates inhibitor depletion and active acid formation.
• Visual Inspection: The fluid should remain a clear viscous liquid. Brown or black fluid indicates active iron corrosion and requires an immediate system flush.

Frequently Asked Questions